Gamestop trade in value help? 11 points for help?

[bendover]

I got a white 120gb xbox with a blue afterglow controller and HDMI input. How much will I get for these? I'm also a pro member if that helps? I'm just too lazy to call or go get it appraised.
P.S.
I'm wondering the value in store credit. Also if there's any promo for turning in a system, warn a brotha.